Method of producing molten pig iron or molten steel pre-products and a plant therefor

ABSTRACT

A plant is provided for producing molten pig iron or molten steel pre-products from lumpy, iron-ore-containing charging substances. The plant comprises a reduction shaft furnace for receiving lumpy, iron-ore-containing charging substances, the plant including a melter gasifier for receiving the reduction product formed in the reduction shaft furnace. The plant also includes a first charging device for at least one of iron ore and ore dust and a second charging device for solid carbon carriers, the melter gasifier being provided with a device for flow-connecting the first charging device for at least one of iron ore and ore dust and the second charging device for charging carbon carriers to at least one dust burner.

This is a division of application Ser. No. 08/066,505, filed May 20,1993, now U.S. Pat. No. 5,445,668.

The invention relates to a method of producing molten pig iron or moltensteel pre-products from lumpy, iron-ore-containing charging substanceswhich are reduced in a reduction shaft furnace by means of a reducinggas, wherein the reduced iron particles obtained are melted in a meltergasifier under supply of coal and oxygen-containing gas undersimultaneous formation of the reducing gas, and the reducing gas issupplied to the reduction zone of the shaft furnace, as well as to aplant for carrying out the method.

A method of this type as well as a plant for carrying out this methodare known from EP-B-0 010,627, AT-B-378,970 as well as AT-B-381,116. Thespecial advantage of such a method is that the use of iron-containingmaterial of a very wide size spectrum, in particular in the rangebetween 10 and 30 mm, as well as the use of carbon carriers of widelyvarying carbon contents are possible without complex measures, and thata sufficient energy supply is ensured without the danger of asimultaneous re-oxidation of the charge. Even coals having high ashcontents and high portions of volatile components may be used withoutany problems.

From AT-B-381,116 it is known to provide for an additional heat supplyfor the melter gasifier by burning coal particles separated from thereducing gas, if non-metallurgical coal is being used.

The present invention has as its object to further develop theabove-described method in so far that also fine ore and/or ore just,such as oxidic iron fine dust incurred in a metallurgical plant, can beused, i.e. preferably in an amount corresponding to from 20 to 30% ofthe normal oxidic iron charge of the above-described method.

According to the invention, this object is achieved in that in additionto the charging substances fine ore and/or ore dust, such as oxidic ironfine dust incurred in a metallurgical plant, is used, the fine oreand/or the ore dust being supplied with solid carbon carriers to atleast one dust burner working into the melter gasifier and being reactedin a substoichiometric combustion reaction.

What is essential in this connection is that combustion in the dustburner is effected such that no components interfering with the processare formed, i.e. it must be ensured that the combustion reactionproceeds substoichiometrically according to the chemical equation

    C+1/2O.sub.2 →CO-111 kJ/mol

and not according to the equation

    C+O.sub.2 →CO.sub.2 -395 kJ/mol,

because the CO₂ is undesired for the reduction of the oxidic Fe dusts.The CO forming subsequently merges into the process gas and theliquefied dust particles merge into the slag or into the pig iron bathof the melter gasifier. For this purpose operation of the burner must beadjusted such that the molar oxygen-fuel ratio, O₂ to C here, is morethan 0.5, preferably is 0.6.

The method according to the invention allows for the processing of alliron fine ores, as they are incurred during transportation and otherwisein a metallurgical plant, and an agglomeration, which hitherto has beencommon, can be obviated.

An advantageous variant of the method according to the invention ischaracterised in that the reducing gas is cooled and dedusted and thatthe dust separated from the reducing gas is returned into the meltergasifier via the dust burner commonly with the fine ore or the ore dustand the solid carbon carriers.

To obtain a thorough mixing and pre-heating and a pre-reduction of themixture of fine ore with carbon carriers, according to a preferredembodiment the-fine ore or the ore dust is charged into the unpurifiedreducing gas obtained from the melter gasifier and pre-heated andpre-reduced in the latter, whereupon the fine ore or the ore dust isseparated commonly with the dust of the reducing gas from the latter andis supplied to the dust burner.

Suitably, the solid carbon carriers are added to the reducing gascommonly with the fine ore or the ore dust.

Another advantageous variant is characterised in that the solid carboncarriers are supplied directly to the dust burner, which results in aslighter influcence on the recycling of the dusts separated from thereducing gas to the melter gasifier.

To eliminate such an influence entirely, advantageously the fine ore orthe ore dust is directly supplied to the dust burner commonly with thesolid carbon carriers.

To obtain a thorough mixing of the fine ore with the carbon carriers andwith the dusts separated from the reducing gas without substantiallyinfluencing the system which separates the dusts, according to apreferred embodiment the fine ore or the ore dust is commonly suppliedwith the solid carbon carriers to the dust burner, together with thedust separated from the reduction gas, via a pressure compensationsluice system preceding the dust burner.

To prevent degassing products from forming in the system separating thedusts from the reducing gas, advantageously coke is used as the solidcarbon carrier.

When directly supplying the carbon carriers to the dust burner, suitablycoal, in the method according to claim 1 in particular coal dustincurred is used as the solid carbon carrier.

A plant for carrying out the method

with a reduction shaft furnace for lumpy iron ore and

with a melter gasifier to receive the reduction product formed in thereduction shaft furnace,

is characterised in that a fine ore or ore dust charging means as wellas a charging means for solid carbon carriers are flow-connected with atleast one dust burner or the melter gasifier.

A preferred embodiment is characterised in that a gas duct carrying offreducing gas from the melter gasifier is provided with a cyclone andenters into the reduction shaft furnace, the cyclone being in flowconnection with the dust burner of the melter gasifier via a sluicesystem, a dust conveying device, such as an injector, and via aconveying duct, and wherein a charging duct originating from the fineore or ore dust charging means enters into the gas duct which isprovided between the melter gasifier and the cyclone, and whereinadvantageously the charging means for solid carbon carriers is inflow-connection with the charging duct for fine ore or ore dust.

Another suitable embodiment is characterised in that a separate chargingduct originates from the charging means for solid carbon carriers andenters directly into the conveying duct which connects the dustconveying device with the dust burner.

A further advantageous embodiment is characterised in that a gas ductcarrying off reducing gas from the melter gasifier is provided with acyclone and enters into the reduction shaft furnace, wherein the cycloneis in flow connection with the dust burner of the melter gasifier via asluice system, a dust conveying device, such as an injector, and via aconveying duct, and wherein a charging duct common to the fine or or theore dust charging means and the charging means for carbon carriersenters into the sluice system between the cyclon and the dust burner.

Advantageously, a gas duct carrying off reducing gas from the meltergasifier is provided with a cyclone and enters into the reduction shaftfurnace, wherein the cyclone is in flow-connection with the dust burnerof the melter gasifier via a sluice system, a dust conveying device,such as an injector, and via a conveying duct, and wherein a chargingduct common to the fine ore or ore dust charging means and the chargingmeans for carbon carriers enters into the conveying duct between thedust conveying device and the dust burner.

The invention will now be explained in more detail by way of severalexemplary embodiments illustrated in the drawings, wherein

FIG. 1 is a schematical illustration of a plant for carrying out themethod of the invention according to a first embodiment, and

FIGS. 2, 3 and 4 show further embodiments in analogous illustrations.

A reduction means designed as a shaft furnace is denoted by 1, intowhose reduction zone lumpy iron oxide-containing charging substances,possibly together with fluxes., are top-charged via a supply duct 2. Theshaft furnace 1 is connected with a melter gasifier 3, in which areducing gas is produced from carbon carriers and an oxygen-containinggas, which reducing gas is supplied to the shaft furnace 1 via a gasduct 4 and which rises in counterdirection to the flow of the sinkingiron ore and causes the reduction of the iron ore. In the gas duct 4, agas purification means 5 is provided, which is designed as a hot gascyclone. To cool the reducing gas, a cooling gas duct 6 enters into thegas duct 4, before the gas duct 4 enters into the hot gas cyclone 5.

The melter gasifier 3 comprises a supply means 7 for solid, lumpy carboncarriers, and a supply duct 8 for an oxygen-containing gas. Within themelter gasifier 3, molten slag and molten pig iron collect below themeltdown gasifying zone 9, which are tapped separately via one separatetap 10, 11, each, or via a common tap 10', as illustrated in FIGS. 2, 3and 4.

The lumpy ore which has been reduced in the shaft furnace 1 in thereduction zone thereof, is supplied to the melter gasifier 3 commonlywith the fluxes burned in the reduction zone via ducts 12 which connectthe shaft furnace 1 with the melter gasifier 3, for instance by means ofdischarge worms 13. To the upper part of the shaft furnace 1, anoff-duct 14 for the top gas forming in the reduction zone thereof isconnected. Part of the reducing gas is fed as cooling gas in the gasduct 4 after having passed a gas purification means 15.

Via a sluice system 16, the dust separated in the hot gas cyclone 5 istransported to at least one dust burner 17 on the melter gasifier 3, viaan injector 18 operated by nitrogen gas. The sluice system 16 serves toovercome the pressure difference between the hot gas cyclone 5 and thedust burner 17, i.e. between a zone of lower pressure in the hot gascyclone 5 and a zone of higher pressure at the dust burner 17. It isformed by dust containers 19 and slides 20 arranged between the dustcontainers 19--the slides being gas- and material-tight closure means,flat slides 21 as well as at least one dosing means, e.g. a cellularwheel sluice 22 and a stop plug 23. Between the injector 18 and the dustburner, furthermore a ball valve 24 and a further stop plug 23 areprovoded.

According to the embodiment illustrated in FIG. 1, a mixture of cokedust and fine ore and/or ore dust is supplied via a charging duct 25into the gas duct 4 provided between the melter gasifier 3 and the hotgas cyclone 5, mixing, pre-heating and pre-reduction of the suppliedmixture taking place in the hot gas cyclone which then works as areduction cyclone. Due to the use of coke dust, the formation ofdegasing products in the sluice system 16 is avoided. The fine oreand/or the ore dust as well as the coke dust are each supplied viaseparate cellular wheel sluices 26, 27 from storage containers 28, 29 toa common mixing bunker 30, from which the mixture is fed into the gasduct 4 via a sluice system 31 comprised of flat slides 21, dustcontainers 19 and intermediately arranged pressure sluice flaps 20'arranged in the charging duct as well as a further dosing means 22.

A nitrogen supply duct 32 entering into the charging duct 25 is provideddownstream of the further dosing means 22, e.g. a cellular wheel sluice.By aid of the sluice system 31, the pressure difference between themixing bunker 30 and the gas duct 4 is overcome.

The mixture supplied from the hot gas cyclone 5 to the dust burner 17 isreacted by aid of this dust burner 17 in a substoichiometric combustionreaction. The CO forming therein merges with the reducing gas. The dustparticles melting on account of the combustion heat get into the slag orinto the pig iron bath.

According to the embodiment illustrated in FIG. 2, the charging duct 25enters into the sluice system 16 provided between the hot gas cyclone 5and the dust burner 17, i.e. into the last dust container provided inthis sluice system 16. This variant is particularly advantageous iflarger amounts of fine ore are to be charged, wherein influence on thehot cyclone 5 is avoided.

According to the embodiment illustrated in FIG. 3, the charging duct 25enters into the duct 33 between the injector 18 and the dust burner 17,which duct 33 leads from the injector to the dust burner, whereby alsoan influence on the operation of the hot cyclone 5 is avoided. Theparticular advantage of this variant is to be seen in that coal dust maybe used instead of coke dust, since degassing of the coal only occurs inthe melter gasifier and cannot lead to an obstruction of the dust returnin the hot gas cyclone 5 or in the sluice system 16.

According to the embodiment illustrated in FIG. 4, the fine ores and/orthe ore dust are charged, separately from the coal dust, into the gasduct 4 leading into the hot gas cyclone 5 via a charging duct 25, andthe coal dust is charged separately therefrom into duct 33 leading fromthe injector 18 to the gas burner 17, via a spearate charging duct 25',a separate sluice system 31, 31' being provided in each charging duct25, 25' so that an adaptation to the different pressures of gas duct 4and duct 33 is feasible. In this case the advantage of the reduction ofthe ore dust in the hot gas cyclone can be combined with the advantageof coal charging, so that here, like in the variant illustrated in FIG.3, use of the coal dust incurred in the plant from coal sieving and fromthe dedusting plant of coal drying is possible.

By the following example, the method according to the variantillustrated in FIG. 1 is explained in more detail:

The analysis of the dust in the reducing gas at the exit of the meltergasifier was as follows (in % by weight):

    ______________________________________                                                Fe    31.8%                                                                   C     50.5%                                                                   CaO   3.0%                                                                    MgO   0.8%                                                                    SiO.sub.2                                                                           8.3%                                                                    Al.sub.2 O.sub.3                                                                    5.6%                                                            ______________________________________                                    

The dust content of the reducing gas was 150 g/m³ (at normalconditions).

The analysis of the fine ore used (moist values) for ore from SanIsidoro, Brazil, is listed in the following table (in % by weight).

    ______________________________________                                        Fe.sub.2 O.sub.3 (Fe)                                                                              92.02%  (64,41%)                                         CaO                  0.09%                                                    MgO                  0.05%                                                    SiO.sub.2            1.16%                                                    Al.sub.2 O.sub.3     0.47%                                                    MnO                  0.05%                                                    Annealing losses     2.85%                                                    Humidity             3.08%                                                    Balance, other substances                                                                          0.32%                                                    ______________________________________                                    

The core size distribution of the fine ore was (in % by weight)

    ______________________________________                                               <20 μm                                                                              2%                                                                   20-63 μm                                                                           16%                                                                   125-63 μm                                                                          35%                                                                   250-125 μm                                                                         39%                                                                   >250 μm                                                                             8%                                                            ______________________________________                                    

Fine ore in a portion of 30% by weight of the total Fe-charge wascharged and melted.

Analysis of the coke used was as follows (in % by weight):

    ______________________________________                                               C       97.2%                                                                 H       0.12%                                                                 N + O   1.71%                                                                 S       0.97%                                                                 C.sub.fix                                                                             88.1%                                                                 Ash portion                                                                           11.3%                                                          ______________________________________                                    

The pre-reduction of the fine ore in the gas duct 4 and in the hotcyclone 5 amounted to 53% by weight. For the reduction in the dustburner 17, 50 kg of coke and 311 m³ (at normal conditions) O₂ per t offine ore were used.

9.3 t of pig iron/h could be produced at an overall ore charge of 14.8t/h. The pig iron produced in the melter gasifier 3 had the followingcomponents (in % by weight), besides iron:

    ______________________________________                                               C            3.9-4.2%                                                         Si           0.4-0.6%                                                         P            0.012%                                                           Mn           0.1%                                                             S            0.04-0.06%                                                ______________________________________                                    

At the same fine ore charge, coal is charged instead of coke in thevariant illustrated in FIG. 4.

Analysis of the coal charged:

    ______________________________________                                               C       81.4%                                                                 H       4.8%                                                                  N       1.4%                                                                  O       5.8%                                                                  S       0.5%                                                                  C.sub.fix                                                                             62.9%                                                                 Ash portion                                                                           6.2%                                                           ______________________________________                                    

The coal consumption was 376 kg, and the O₂ -consumption was 460 N³ mper t of fine ore.

9.1 t of pig iron/h could be produced at an overall ore charge of 14.5t/h. The pig iron produced in the melter gasifier had the followingcomponents, besides iron:

    ______________________________________                                               C            3.9-4.2%                                                         Si           0.4-0.6%                                                         P            0.01%                                                            Mn           0.1%                                                             S            0.04-0.06%                                                ______________________________________                                    

What we claimed is:
 1. A plant for producing molten pig iron or moltensteel pre-products from lumpy, iron-ore-containing charging substancesof the type includinga reduction shaft furnace for said lumpy,iron-ore-containing charging substances, and a melter gasifier forreceiving the reduction product formed in said reduction shaft furnace,the improvement comprising a first charging means for at least one ofiron ore and ore dust, a second charging means for solid carboncarriers, at least one dust burner provided at said melter gasifier,means for flow-connecting said first charging means for said at leastone of iron ore and ore dust and said second charging means for saidsolid carbon carriers with said at least one dust burner.
 2. A plant asset forth in claim 1, further comprisinga gas duct carrying off reducinggas from said melter gasifier and entering into said reduction shaftfurnace, a cyclone provided in said gas duct, a sluice system precedingsaid at least one dust burner and flow-connected with said cyclone, adust conveying device flow-connected to said sluice system, a conveyingduct flow-connected with said dust conveying device and with said atleast one dust burner, a charging duct departing from said firstcharging means for said at least one of fine ore and ore dust andentering into said gas duct provided between said melter gasifier andsaid cyclone.
 3. A plant as set forth in claim 2, wherein said dustconveying device is an injector.
 4. A plant as set forth in claim 2,further comprising duct means flow-connecting said second charging meansfor said solid carbon carriers with said charging duct for said at leastone of said fine ore and ore dust.
 5. A plant as set forth in claim 2,further comprising a separate charging duct departing from said secondcharging means for said solid carbon carriers and entering directly intosaid conveying duct connecting said dust conveying device with said atleast one dust burner.
 6. A plant as set forth in claim 1, furthercomprisinga gas duct carrying off reducing gas from said melter gasifierand entering into said reduction shaft furnace, a cyclone provided insaid gas duct, a sluice system preceding said at least one dust burnerand flow-connected with said cyclone, a dust conveying deviceflow-connected with said sluice system, a conveying duct flow-connectedwith said dust conveying device and with said at least one dust burner,a charging duct common to both said first charging means for said atleast one of fine ore and ore dust and said second charging means forsaid solid carbon carriers, entering into said sluice system providedbetween said cyclone and said at least one dust burner.
 7. A plant asset forth in claim 1, wherein said dust conveying device is an injector.8. A plant as set forth in claim 1, further comprisinga gas ductcarrying off reducing gas from said melter gasifier and entering intosaid reduction shaft furnace, a cyclone provided in said gas duct, asluice system preceding said at least one dust burner and flow-connectedwith said cyclone, a dust conveying device flow-connected with saidsluice system, a conveying duct flow-connected with said dust conveyingdevice and with said at least one dust burner, a charging duct common toboth said first charging means for said at least one of fine ore and oredust and said second charging means for said solid carbon carriers,entering into said conveying duct provided between said dust conveyingdevice and said at least one dust burner.
 9. A plant as set forth inclaim 8, wherein said dust conveying device is an injector.
 10. A plantas set forth in claim 2, 6 or 8, further comprising a further sluicesystem provided in said charging duct.
 11. A plant as set forth in claim10, wherein said further sluice system provided in said charging ductcomprises at least one pressure sluice flap and a dust container.
 12. Aplant as set forth in claim 11, wherein said further sluice systemcomprises a flat slide.